In normal oil wells, emulsions frequently form, simply by mechanical mixing of reservoir water and oil. Such emulsions generally have a higher viscosity, or resistance to flow into the well bore, and the emulsions accordingly tend to reduce production of oil into or from the well. In enhanced oil recovery from a petroleum reservoir formation by injection fluids frequently form emulsions in the formation. Such emulsions result from the mixture of injected fluids and connate water and oil in the reservoir. Where oil production is from fields of relatively high gravity, such as many California fields, the addition of steam, gas or water as a flooding fluid frequently results in additional emulsification.
It has long been known that certain surface active materials, especially non-ionic surfactants, are effective to break emulsions, particularly after production, as in surface treating of produced fluids. They are also helpful in increasing productivity from a well or in maintaining fluid flow through a formation to the extend that the emulsion is broken.
Almost all earth formations forming petroleum reservoirs are created by sedimentary deposition with subsequent compaction or crystallization of the rock matrix. Such deposition of detrital materials, with varying composition and over extensive geological times, occurs at varying rates. The resulting compacted rocks in which petroleum accumulates are permeable, but in general are heterogeneous. Accordingly, the petroleum reservoir formed by such rock formations are inherently inhomogeneous as to both porosity and permeability for fluid flow, either native (connate) or injected fluids. Furthermore, flow permeability for connate gas, oil and water is substantially different for each liquid or mixture thereof. A particular feature of such inhomogeneity of sedimentary rock formations appears to be their shale or clay content and the susceptibility of such clay to alteration when contacted by water and particularly when such water is injected as steam. In general, clays have large surface area to volume ratios and tend to affect adversely contact between connate oil and reservoir rock. Most specifically, they adversely affect viscous oils containing organo-metallic and acidic components which are particularly susceptible to enhanced oil recovery by steam or gas injection. However, it is also known that either or both of such reservoir conditions may promote formation of viscous emulsions that inhibit or reduce the flow of oil to the producing well. Hence, there is a need for surfactant compositions which reduce the viscosity of emulsions in such formations.
This invention is an improvement over prior methods of using surfactant compositions to enhance petroleum production from oil-bearing formations. Many of these are mentioned and discussed in U.S. Pat. No. 4,086,964. Others include U.S. Pat. Nos. 4,393,937, 4,532,993 and 4,161,217.